Sophie Cornu

Adsorption of arsenic (V) on kaolinite and on kaolinite–humic acid complexes: Role of humic acid nitrogen groups

In order to investigate the influence of organic matter on arsenic retention, we used batch experiments at pH 7 to determine the adsorption of As(V) on three different solids: a crude, purified, Ca-exchanged kaolinite and two kaolinites coated with humic acids (HAs) having different nitrogen contents. We first examined the adsorption of each HA onto kaolinite, and then used the HA-kaolinite complexes to study As(V) adsorption. The results clearly show an influence of the HA coating on As adsorption. For example, with low initial As concentrations the solid/liquid partition coefficient (R(d)) for both HA complexes is greater than that for the crude kaolinite. We found that increasing the initial As concentrations decreased the R(d) values of the HA-coated kaolinites until finally they were the same as the crude kaolinite R(d) values. This suggests that adsorption occurs first on the HA sites and then, once the HA sites are saturated, on the remaining kaolinite sites. We also noted that the more reactive HA-kaolinite complex was the one with the highest N/C ratio. Comparing the amount of amine groups in the HA-kaolinite complexes with the total amount of adsorbed As indicates that the HA amine groups, due to their positive charge at pH 7, play a key role in the adsorption of As onto organic matter.

Evidence of titanium mobility in soil profiles, Manaus, central Amazonia

Titanium minerals are classically considered to be very resistant to weathering in soils. Consequently, variations of titanium concentrations within the soils were used to estimate rates of weathering of parent material. Mobility of Ti was studied in an Amazonian ferralsol using a large set of techniques. Chemical and mineralogical studies of Ti distribution in the soil profile showed that weathering of Ti minerals follows the mineral sequence: ilmenite, pseudorutile, rutile and anatase. This weathering leads to absolute Ti losses on the profile scale. Mineral bags were located at different depths within the top soil, and removed after 6, 12, 18 months in the soil. In all bags the presence of newly generated anatase was recorded after the exposure periods, showing the rapidity of the processes. The vegetation recycles a significant quantity of Ti, increasing Ti mobility in soils. These results indicate that Ti can be mobile under certain conditions and thus should not always be used to estimate weathering rates.

The environmental impact of heavy metals from sewage sludge in ferralsols (São Paulo, Brazil)

The spreading of sewage sludge on acidic ferralsol soil was simulated in a column experiment in order to estimate the potential impact on water and soil quality. Drainage and runoff water were sampled daily over a 2-month experiment and analysed for Fe, Ni, Cu, Pb and DOC. Results show a clear influence of the sludge on the water quality, especially at the start of the experiment, increasing the export of Cu, Ni, Pb and in DOC from the soil, mainly in dissolved form. Nickel was usually the most mobile element in the sludge and in the soil. In the soil, Pb mobility was complex and increased drastically with time compared to the other elements. No significant increase in soil heavy metal content due to the sludge spreading was recorded on this time scale.

Scale of spatial dependence between chemical properties of topsoil and subsoil over a geologically contrasted area (Massif central, France)

This study investigates scale spatial specific dependence of some major and trace element contents in topsoil horizons and in alterite type horizons (subsoil horizons) over a weakly contaminated area. The study seeks also to compare the spatial distributions of chemical elements at both depths to the spatial variability of the alterite type in order to examine the effect of the parent material. The probability of occurrence of alterite type was estimated using indicator kriging (IK). Factorial kriging analysis (FKA) was used to analyze spatial variability in some soil chemical properties (Ca, Mg, K, Fe, Cr and Co) measured at two depths over a geologically contrasted area of 10 ha in central of France. The coefficients of the coregionalization matrix at different spatial scales reveal the dominant long-range autocorrelation and cross-correlation in all chemical elements in both depths except for trace elements (Co and Cr) where the short-range structure dominates the cross-correlation. The resulting structural correlation coefficients showed strong correlations between variables changing as a function of spatial scale. These relationships between chemical properties at different spatial scales were not revealed by the linear correlation coefficients. A principal component analysis was performed on the coregionalization matrices at each depth to summarize the relationships among the variables at the different spatial scales. Cokriging allowed mapping each spatial component for both depths. These maps were then compared with the probability map of alterite type estimated using indicator kriging. This comparison revealed that the spatial pattern of chemical elements in the subsoil horizons is almost certainly due to the alterite type effect, whereas the alterite type effect on the spatial pattern of chemical properties in the topsoil horizons was partly hidden by human activities and erosion.

Effect of Agricultural Practices on Trace‐Element Distribution in Soil

Abstract The impact of agricultural practices on the spatial distribution of trace elements (TEs) in the surface horizon of Albeluvisols was studied by comparing three types of situation with an increasing anthropogenic gradient: a forest soil, considered as a reference, and cultivated soils with and without spreading of sewage sludge. Total cadmium (Cd), cobalt (Co), chromium (Cr), copper (Cu), nickel (Ni), lead (Pb), and zinc (Zn) were determined in soil surface horizons. The quantity of particles finer than 2 µm, organic carbon (OC), iron (Fe), manganese (Mn), and calcium (Ca) contents were also measured and used as tracers of soil components that may have contained TEs. Governing factors of the spatial variability of TEs were searched for through comparison of the descriptive statistics (mean and coefficient of variation) and the determination of the best multivariate model predicting TE contents. Nickel and Cr distributions seem to be mainly linked to variability of the parent material composition, whereas that of Co is related to redox pedological processes. In addition, agricultural practices play a role in TE distribution, through the input of TEs, mostly Cd, Cu, and Zn, via sewage sludge spreading and liming amendments, and lateral (homogenization) and vertical (mixing of horizons) redistribution through tilling the soil.

Soil drainage as an active agent of recent soil evolution: a review.

Abstract While research on pedogenesis mainly focuses on long-term soil formation and most often neglects recent soil evolution in response to human practices or climate changes, this article reviews the impact of artificial subsurface drainage on soil evolution. Artificial drainage is considered as an example of the impact of recent changes in water fluxes on soil evolution over time scales of decades to a century. Results from various classical studies on artificial drainage including hydrological and environmental studies are reviewed and collated with rare studies dealing explicitly with soil morphology changes, in response to artificial drainage. We deduce that soil should react to the perturbations associated with subsurface drainage over time scales that do not exceeding a few decades. Subsurface drainage decreases the intensity of erosion and must i) increase the intensity of the lixiviation and eluviation processes, ii) affect iron and manganese dynamics, and iii) induce heterogeneities in soil evolution at the ten meter scale. Such recent soil evolutions can no longer be neglected as they are mostly irreversible and will probably have unknown, but expectable, feedbacks on crucial soil functions such as the sequestration of soil organic matter or the water available capacity.

Tracing contamination sources in soils with Cu and Zn isotopic ratios

Copper (Cu) and zinc (Zn) are naturally present and ubiquitous in soils and are important micronutrients. Human activities contribute to the input of these metals to soils in different chemical forms, which can sometimes reach a toxic level for soil organisms and plants. Isotopic signatures could be used to trace sources of anthropogenic Cu and Zn pollution. The aim of this paper is to determine whether it is possible to identify (i) Cu and Zn contamination in soils and their sources, on the basis of their isotopic signatures, and (ii) situations that are a priori favorable or not for tracing Cu and Zn pollution using the isotopic approach. Therefore, we compiled data from the literature on Cu and Zn isotopes in soils, rocks and pollutants and added to this database the results of our own research. As only a few studies have dealt with agricultural contamination, we also studied a soil toposequence from Brittany, France, that experienced spreading of pig slurry for tens of years. In the surface horizons of the natural soils, the δ(65)Cu values vary from -0.15 to 0.44‰ and the δ(66)Zn from -0.03 to 0.43‰. Furthermore, vertical variations along soil profiles range from -0.95 to 0.44‰ for δ(65)Cu and from -0.53 to 0.64‰ for δ(66)Zn values. We concluded that pedogenetic processes can produce isotopic fractionation, yet, it is not always discernible and can be overprinted by an exogenous isotopic signature. Furthermore, some contaminants are enriched in heavy Cu or in light Zn compared to the rock or soil, but no generalization can be made. The anthropogenic inputs can be identified based on stable Cu and Zn isotope ratios if the isotope ratios of the sources are different from those of the soil, which needs to be tested for each individual case.

Quantification of soil volumes in the Eg & Bt-horizon of an Albeluvisol using image analysis

In this study, we provide a strategy to quantify the effects on soil evolution of driving forces such as human activities or global change. This strategy was developed for situations in which soil evolution resulted in the formation of a complex juxtaposition of soil volumes with distinct properties including soil colours. It is based on image analysis. Our approach proceeds in two steps: (1) to find the minimum sample size over which the soil anisotropy can be neglected and (2) to define a Representative Elementary Volume (REV) of that sample. This approach was developed on the Eg & Bt horizon of a drained Albeluvisol in which three decimetric soil monoliths were sampled at 60, 110 and 210 cm from a drain. The monoliths were sliced into 1.5-cm horizontal layers. Each slice was photographed and studied by image analysis. At the monolith scale, there was neither lateral nor vertical anisotropy. The sampled monoliths were larger than the REV allowing quantification of the different soil volumes constituting...

Location of Trace Elements in Unpolluted Soils by a Combined Method

Abstract A sequential extraction procedure was combined with physical fractionation and mineralogy to determine the distribution of trace elements (TE) among the different phases of a poorly weathered sample. It was first fractionated into five particle‐size fractions. Two of these were selected for sequential extractions on the basis of their contrasting mineralogical compositions. A five‐step sequential extraction scheme was employed. The studied sample is mostly composed of hornblende, quartz, and feldspars. Early weathering has already occurred, resulting in the formation of smectite and oxides. Sequential extractions show that the studied elements are mostly associated with the residual phases. Hornblende was the main TE bearer of the primary minerals, whereas TEs released through weathering precipitated in both smectite and oxides. Oxides were found to scavenge copper (Cu) and cobalt (Co) more efficiently than smectite. Copper and nickel (Ni) were more concentrated in smectite than in hornblende.

Impact of carbo-gaseous saline waters registered by soils

Abstract The impact of carbo-gazeous saline spring waters, rich in Ca, Fe, As and P and chemically stable through time, on the chemistry (major and trace elements) and mineralogy of soils developed from anatexite is presented. The soils developed beyond the influence of the spring are typical of a granite pedogenesis on a granitic bedrock with Ca loss, Si, Al and K conservation. The soils influenced by the springs are enriched in Ca and Fe, respectively, precipitated as carbonates and oxides. In such soils, the presence of two Ca-enrichment peaks may be explained by the occurrence of two distinct precipitation mechanisms for the carbonates: (1) related to degassing of the carbo-gaseous waters upon emergence at the surface, and (2) in the water-unsaturated zone, related to capillary rise and evaporation processes. The precipitation of iron oxides is related to a change in the redox potential of the mineral waters, following their emergence at the surface. The simultaneous association of As+P with Fe, as evidenced by principal components analysis and in the patterns in concentrations vs. depth observed in soils, can be explained by adsorption and/or coprecipitation of As and P during iron-oxide formation, while The As and P enrichments and the carbonate formation are independent. The extent of the spring influence was studied: the soil enrichments in Ca and, particularly, Fe sharply decrease with increasing distance from the spring on a metric scale.